A low-ripple BLDC drive circuit and method of operation thereof

Abstract

The embodiment of the application discloses a low-ripple BLDC driving circuit and a working method thereof. The circuit comprises a control unit, an RLC switching circuit connected between a three-phase bridge inverter circuit and a three-phase direct current motor, and the control unit is connected with the RLC switching circuit and the three-phase bridge inverter circuit respectively. The RLC switching circuit comprises at least three RLC switching units, and the three-phase output end of the three-phase bridge inverter circuit is connected with the three-phase direct current motor through the RLC switching units respectively. The circuit of the embodiment of the application can solve the problem that when the PWM control strategy is used to control the three-phase bridge inverter driving circuit to drive the direct current motor, the switch tube on-off and commutation pulse current, driving current ripple, torque ripple and noise are too large due to the small direct current motor armature inductance, and the difficulty and cost of the selection of the switch tube and the control method are increased.

Description

Technical Field

[0001] This invention relates to the field of motor drive circuit technology, and in particular to a low-ripple BLDC drive circuit and its operating method. Background Technology

[0002] If the internal circuit of a DC motor is equivalent to an ideal circuit, it is equivalent to each phase consisting of a resistor, an inductor, and an electromotive force connected in series. For example... Figure 1 As shown, R U R V R W The equivalent armature resistances of phases U, V, and W are respectively, and LM is the equivalent armature inductance of phases three. U e V e W These are the back electromotive forces of the three phases U, V, and W, respectively.

[0003] The traditional approach to driving three-phase DC motors is to use a direct drive scheme with a three-phase bridge inverter circuit. Using PWM modulation, the uncertainty of the armature inductance L in the U, V, and W phases of the DC motor often affects its normal operation: if the armature inductance L is too small, large pulse currents will occur during switching and commutation, resulting in significant ripple in the drive current, increased load on the switching transistors, and greater torque pulsation and noise in the DC motor, affecting the stability and reliability of the drive circuit, and in severe cases, jeopardizing motor safety. Traditional solutions include adjusting the bus voltage and adjusting the switching frequency of the switching transistors. Adjusting the bus voltage requires adding a BUCK circuit topology before the three-phase bridge inverter circuit to control the output voltage; this method is complex, difficult to control, and relatively expensive. Adjusting the switching frequency usually involves increasing the switching frequency, which increases transistor losses and reduces overall circuit efficiency.

[0004] Therefore, it is necessary to design a new circuit to solve the problems of increased difficulty and cost in controlling a DC motor using a three-phase bridge inverter drive circuit with a PWM control strategy. These problems include excessive pulse current, drive current ripple, torque pulsation, and noise during switching and commutation of the switching transistors due to the small armature inductance of the DC motor, as well as the selection of switching transistors and control methods. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a low-ripple BLDC drive circuit and its working method.

[0006] To solve the above technical problems, the purpose of the present application is realized by the following technical solutions: a low ripple BLDC driving circuit is provided, comprising: a control unit, an RLC switching circuit connected between a three-phase bridge inverter circuit and a three-phase DC motor, the control unit is connected with the RLC switching circuit and the three-phase bridge inverter circuit respectively; wherein the RLC switching circuit comprises at least three RLC switching units, and the three-phase output end of the three-phase bridge inverter circuit is connected with the three-phase DC motor through the RLC switching units respectively.

[0007] Further technical solutions are: the RLC switching unit comprises a switching tube, a power resistor, an inductor, an absorption resistor and an absorption capacitor; the switching tube comprises a first switching tube, a second switching tube, a third switching tube, a fourth switching tube and a fifth switching tube, the first switching tube is connected with the power resistor in series; the absorption resistor and the absorption capacitor are connected in series; the second switching tube and the third switching tube are connected in series, and one end of the inductor is connected between the second switching tube and the third switching tube; the fourth switching tube and the fifth switching tube are connected in series, and the other end of the inductor is connected between the fourth switching tube and the fifth switching tube; after the power resistor is connected with the first switching tube in series, the power resistor is connected with the second switching tube and the third switching tube connected in series, the fourth switching tube and the fifth switching tube connected in series, and the absorption resistor and the absorption capacitor connected in series in parallel, and then connected with the three-phase bridge inverter circuit and the three-phase DC motor; the switching tube is connected with the control unit.

[0008] Further technical solutions are: the switching tube is a complementary metal-oxide-semiconductor (CMOS) tube.

[0009] Further technical solutions are: the switching tube comprises two connected NMOS tube discrete devices.

[0010] Further technical solutions are: the switching tube comprises a common-source NMOS tube integrated device.

[0011] Further technical solutions are: the three-phase bridge inverter circuit comprises switching tubes VT1, VT2, VT3, VT4, VT5 and VT6; the switching tubes VT1 and VT4 are connected in series; the switching tubes VT2 and VT5 are connected in series; the switching tubes VT3 and VT6 are connected in series; one end of one of the RLC switching units is connected between the switching tubes VT1 and VT4; one end of another RLC switching unit is connected between the switching tubes VT2 and VT5; one end of a third RLC switching unit is connected between the switching tubes VT3 and VT6.

[0012] The further technical scheme is that the control unit comprises a PWM control chip.

[0013] In addition, the technical problem to be solved by the present application is also to provide a working method of the low-ripple BLDC driving circuit, comprising:

[0014] The low-ripple BLDC driving circuit turns on two phases in the three-phase bridge inverter circuit each time; when two phases in the three-phase bridge inverter circuit are turned on, the switch tube connected in series with the power resistor in the corresponding connected RLC switch unit is turned off, one switch tube is turned on at each end of the inductor and the two switch tubes are in a non-series connection, the inductor suppresses the pulse current, and the absorbing resistor and the absorbing capacitor are transiently operated.

[0015] The further technical scheme is that the low-ripple BLDC driving circuit further comprises:

[0016] When one phase in the three-phase bridge inverter circuit is cut off, the switch tube connected in series with the power resistor in the corresponding connected RLC switch unit is turned on, one switch tube is turned on at each end of the inductor and the two switch tubes are in a non-series connection, and the power resistor consumes the energy stored by the inductor.

[0017] The further technical scheme is that the two phases in the three-phase bridge inverter circuit are turned on by turning on the corresponding switch tubes in the three-phase bridge inverter circuit, and the two phases in the three-phase bridge inverter circuit are cut off by cutting off the corresponding switch tubes in the three-phase bridge inverter circuit.

[0018] The beneficial effects of the present application compared with the prior art are that: the present application sets the control unit, the RLC switch circuit connected between the three-phase bridge inverter circuit and the three-phase DC motor, and the RLC switch unit connected between each phase and the three-phase DC motor, when the phase is turned on, the inductor in the RLC switch unit suppresses the pulse current, the absorbing resistor and the absorbing capacitor are transiently operated, when the phase is turned off, the power resistor consumes the energy released by the inductor, and the problems of too small armature inductance of the DC motor, too large pulse current, driving current ripple, torque ripple and noise during switching and commutation of the switch tube, and the increase of difficulty and cost of the selection of the switch tube and the control method are solved.

[0019] The present application will be further described below in combination with the drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical scheme of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below, and obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0021] Figure 1 A schematic diagram of an equivalent circuit of a DC motor provided by the prior art;

[0022] Figure 2 A schematic diagram of a three-phase bridge inverter driving circuit provided by the prior art;

[0023] Figure 3 A schematic block diagram of a low-ripple BLDC driving circuit provided by an embodiment of the present application;

[0024] Figure 4 A specific circuit schematic diagram of a low-ripple BLDC driving circuit provided by an embodiment of the present application;

[0025] Figure 5 A specific circuit schematic diagram of an RLC switching circuit provided by an embodiment of the present application;

[0026] Figure 6 A U-phase phase current schematic diagram provided by an embodiment of the present application;

[0027] Identified explanation in the figure:

[0028] 10, control unit; 20, three-phase bridge inverter circuit; 30, three-phase DC motor; 40, RLC switching circuit. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0030] It should be understood that when used in the specification and the appended claims, the terms "comprise" and "include" indicate the presence of described features, integers, steps, operations, elements, and / or components, but do not exclude one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0031] It should also be understood that the terms used in the present application specification are only for the purpose of describing specific embodiments and are not intended to limit the present application. As used in the present application specification and the appended claims, unless otherwise clearly indicated by the context, the singular forms "a", "an" and "the" are intended to include the plural forms.

[0032] It should be further understood that the term "and / or" as used in the specification and in claims of the application, means any combination of one or more of the associated listed items and all possible combinations, and includes these combinations.

[0033] Referring to Figure 3 , Figure 3 A schematic block diagram of a low-ripple BLDC driving circuit is provided for an embodiment of the application, which can be applied in the driving process of a direct current motor, to solve the problems of too large pulse current, driving current ripple, torque ripple and noise, and the increase of difficulty and cost of selection of switching tube and control method, etc. when using PWM control strategy to control the three-phase bridge inverter driving circuit to drive the direct current motor due to too small armature inductance of the direct current motor.

[0034] Referring to Figure 3 The above-mentioned low-ripple BLDC driving circuit comprises a control unit 10 and an RLC switching circuit 40 connected between a three-phase bridge inverter circuit 20 and a three-phase direct current motor 30, the control unit 10 is connected with the RLC switching circuit 40 and the three-phase bridge inverter circuit 20 respectively; wherein the RLC switching circuit 40 comprises at least three RLC switching units, and the three-phase output end of the three-phase bridge inverter circuit 20 is connected with the three-phase direct current motor 30 through the RLC switching units respectively.

[0035] Compared with the driving circuit shown in Figure 2 , the driving circuit of the embodiment connects at least one RLC switching unit between the three-phase output end of the three-phase bridge inverter circuit 20 and the three-phase direct current motor 30, uses the RLC switching unit to reduce the impact on the switching tube connected in the phase and on the three-phase direct current motor 30 when the phase is turned on, and stores the impact in the inductance; when the phase is turned off, the energy stored in the inductance can be consumed, the decline of the phase current of the corresponding phase is delayed, and the impact on the switching tube connected in the phase and on the three-phase direct current motor 30 when the phase is turned off is reduced.

[0036] In an embodiment, referring to Figure 4 and Figure 5The RLC switch unit comprises a switch tube, a power resistor, an inductor, an absorption resistor and an absorption capacitor. The switch tube comprises a first switch tube, a second switch tube, a third switch tube, a fourth switch tube and a fifth switch tube. The first switch tube is connected in series with the power resistor. The absorption resistor is connected in series with the absorption capacitor. The second switch tube is connected in series with the third switch tube, and one end of the inductor is connected between the second switch tube and the third switch tube. The fourth switch tube and the fifth switch tube are connected in series, and the other end of the inductor is connected between the fourth switch tube and the fifth switch tube. The power resistor is connected in parallel with the second switch tube and the third switch tube, the fourth switch tube and the fifth switch tube and the absorption resistor and the absorption capacitor in sequence, and is connected with a three-phase bridge inverter circuit 20 and a three-phase DC motor 30 in parallel. The switch tube is connected with the control unit 10.

[0037] In the embodiment, the switch tube can be but is not limited to a top switch tube.

[0038] In the embodiment, the switch tube can comprise two connected NMOS tube discrete devices.

[0039] In another embodiment, the switch tube can comprise a common-source NMOS tube integrated device.

[0040] As shown in Figure 4 The switch tube connected in series with the power resistor specifically refers to switch tubes VT7, VT12 and VT17. Resistors R1, R3 and R5 are power resistors; resistors R2, R4 and R6 are absorption resistors, and capacitors C1, C2 and C3 are absorption capacitors.

[0041] In an embodiment, referring to Figure 4 The three-phase bridge inverter circuit 20 comprises switch tubes VT1, VT2, VT3, VT4, VT5 and VT6. The switch tubes VT1 and VT4 are connected in series. The switch tubes VT2 and VT5 are connected in series. The switch tubes VT3 and VT6 are connected in series. One end of one of the RLC switch units is connected between the switch tubes VT1 and VT4. One end of another RLC switch unit is connected between the switch tubes VT2 and VT5. One end of a third RLC switch unit is connected between the switch tubes VT3 and VT6.

[0042] In the embodiment, the switch tubes VT1, VT2, VT3, VT4, VT5 and VT6 can be MOSFET, IGBT and other power tube discrete devices, or MOSFET, IGBT power tube integrated modules.

[0043] In the embodiment, as shown in Figure 4 The plurality of RLC switching units are respectively loaded between the U, V, W three-phase output terminals of the traditional three-phase bridge inverter circuit 20 and the three-phase DC motor 30M1; for example, one of the RLC switching units is connected between the switch tubes VT1 and VT4, another RLC switching unit is connected between the switch tubes VT2 and VT5, and a third RLC switching unit is connected between the switch tubes VT3 and VT6; the outputs of the three RLC switching units are respectively connected to the three-phase circuit of the three-phase DC motor 30M1; the RLC switching unit is composed of four parallel paths, and the order from the positive electrode to the negative electrode is: the first path is the pair of top switch tubes VT7 and the power resistor R1 in sequence, the second path is the pair of top switch tubes VT8 and VT11 in sequence, one end of the inductor L1 is connected between VT8 and VT11, the third path is the pair of top switch tubes VT9 and VT10 in sequence, the other end of the inductor L1 is connected between VT9 and VT10, and the fourth path is the absorption resistor R2 and the absorption capacitor C1 in sequence.

[0044] In the embodiment, the first switch tube refers to the switch tubes VT7, VT12, and VT17; the second switch tube refers to the switch tubes VT8, VT13, and VT18; the third switch tube refers to the switch tubes VT11, VT16, and VT21; the fourth switch tube refers to the switch tubes VT9, VT14, and VT19; and the fifth switch tube refers to the switch tubes VT10, VT15, and VT20.

[0045] In an embodiment, referring to Figure 4 The control unit 10 described above includes a PWM control chip, such as an STM32F405.

[0046] In actual use, according to the working mode of the DC motor, the low-ripple BLDC driving circuit turns on two of U, V, and W phases each time.

[0047] When U and V phases are turned on, at the turn-on moment, the U-phase switch tubes VT8 and VT10 in the RLC switching units of the V and U phases are turned on, the V-phase switch tubes VT13 and VT15 are turned on, the inductors L2 and L1 suppress the pulse current, the absorption resistors R4 and R2 and the absorption capacitors C2 and C1 are transiently actuated, the impact on the switch tubes VT1, VT4, VT2, and VT5 and on the three-phase DC motor 30M1 is reduced, the switch tubes VT17, VT19, and VT21 of the W phase are turned on, the energy stored in the inductor L3 is released, and the power resistor R5 consumes the energy. At the turn-off moment, the energy stored in the inductors L2 and L1 corresponding to the V and U phases is released, thereby reducing the ripple current of the driving current, reducing the torque ripple and noise of the DC motor.

[0048] When V and W phases are conducted, at the instant of conduction, V-phase switch tubes VT13, VT15 in the RLC switching unit of V phase and W-phase switch tubes VT18, VT20 are conducted, the inductances L2, L3 inhibit pulse current, the absorbing resistors R4, R6 and the capacitors C2, C3 are transiently operated to reduce the impact on the switch tubes VT2, VT5, VT3, VT6 and on the three-phase DC motor 30M1; the switch tubes VT7, VT9, VT11 of U phase are conducted, the energy stored in the inductance L1 is released, and the power resistor R1 consumes the energy. At the instant of turn-off, the energy stored in the inductances L2, L3 of V and W phases is released, thereby reducing the ripple current of the driving current, the torque ripple and noise of the DC motor are reduced.

[0049] When U and W phases are conducted, at the instant of conduction, U-phase switch tubes VT8, VT10 in the RLC switching unit of U phase and W-phase switch tubes VT18, VT20 are conducted, the inductances L1, L3 inhibit pulse current, the resistors R2, R6 and the capacitors C1, C3 are transiently operated to reduce the impact on the switch tubes VT1, VT4, VT3, VT6 and on the motor M1; the switch tubes VT12, VT14, VT16 of V phase are conducted, the energy stored in the inductance L2 is released, and is mainly consumed by the power resistor R3. At the instant of turn-off, the energy of the inductances L1, L3 of U and W phases is released, delaying the decline of the U and W phase currents, reducing the ripple current, and reducing the torque ripple and noise of the DC motor.

[0050] As shown in Figure 4 and Figure 5 Taking the U phase and the corresponding RLC switching unit as an example, when the U phase is conducted, the switch tubes VT8, VT10 in the RLC switching unit are conducted, and the switch tubes VT7, VT9, VT11 are opened, the inductance L1 inhibits pulse current, the absorbing resistor R2 and the absorbing capacitor C1 in the absorbing circuit are transiently operated to reduce the impact on the switch tubes VT1, VT4 and on the three-phase DC motor 30M1 when conducted; when the U phase is turned off, the switch tubes VT7, VT9, VT11 are conducted, so that the current direction in the inductance is always consistent with the circulating direction, improving the energy utilization rate of the inductance, and part of the energy stored in the inductance L1 continues to be transmitted to the motor, while the power resistor R1 consumes part of the energy stored in the inductance L1, delaying the decline of the U phase current, and reducing the impact on the switch tubes VT1, VT4 and on the three-phase DC motor 30M1 when turned off.

[0051] As shown in Figure 6Fig. 1 is a schematic diagram of the U-phase phase current waveform of the prior art three-phase bridge inverter drive circuit and the low-ripple BLDC drive circuit in operation. Among them, H_PWM-L_ON indicates that the upper switch tube of U, V, and W three-phase adopts PWM control (fixed duty cycle is 0.5), and the lower switch tube adopts straight-through control (always on), PWM_UH, PWM_VH, and PWM_WH are respectively the PWM control signals of the upper tube of U, V, and W phase; PWM_UL, PWM_VL, and PWM_WL are respectively the straight-through control signals of the lower tube of U, V, and W phase; I U is the U-phase phase current; 0°, 60°, 120°, 180°, 240°, 300°, and 360° are the electrical angles of the motor rotor. The motor rotor is driven by the drive circuit once every 60°. By comparing the similarities and differences of the U-phase phase current of the traditional three-phase bridge inverter drive circuit and the low-ripple BLDC drive circuit, it can be seen that the same points of the drive circuit of the prior art and the drive circuit of the embodiment are: the U-phase phase current change trend is consistent, and the waveform appears a small downward bias at the lower tube commutation instant and thereafter. The difference lies in: at the rotor electrical angles of 0° and 180°, the U-phase phase current of the prior art three-phase bridge inverter drive circuit has a large pulse current, and the pulse current of the circuit of the embodiment is smaller; at the rotor electrical angles of 0°-120° and 180°-300°, the U-phase phase current ripple current of the circuit of the embodiment is smaller than that of the U-phase phase current ripple current of the prior art three-phase bridge inverter drive circuit; at the rotor electrical angles of 120° and 300°, the U-phase phase current of the prior art three-phase bridge inverter drive circuit has a longer falling time than the U-phase phase current of the drive circuit of the embodiment.

[0052] In summary, the method of the embodiment reduces the torque ripple and noise of the DC motor, improves the reliability and stability of the drive system; reduces the pulse current during on-off commutation, reduces the drive ripple current, to a certain extent, weakens the impact on the switch tube and the motor, improves the safety of the drive system; relatively reduces the selection requirements of the switch tube and the motor, thereby saving part of the cost. It can reduce the pulse current during on-off and commutation, the drive current ripple, the torque ripple and noise of the DC motor, reduce the working burden of the switch tube and the DC motor, thereby improve the stability, reliability and safety of the drive system.

[0053] The low-ripple BLDC drive circuit described above, by setting the control unit 10, the RLC switch circuit 40 connected between the three-phase bridge inverter circuit 20 and the three-phase DC motor 30, in the phase conduction, by the inductance in the RLC switch unit inhibits the pulse current, the absorption resistance absorbs the transient action of the capacitor, in the phase off, using the power resistance to consume the energy released by the inductance, to solve the problem of using PWM control strategy to control the three-phase bridge inverter drive circuit to drive the DC motor, because the armature inductance of the DC motor is too small, resulting in excessive pulse current, drive current ripple, torque ripple and noise when the switch tube is turned on and off and commutates, and the difficulty and cost of the selection of the switch tube and the control method are increased.

[0054] In an embodiment, a method for operating the low-ripple BLDC drive circuit described above is also provided, comprising:

[0055] The low-ripple BLDC drive circuit turns on two phases in the three-phase bridge inverter circuit 20 each time; when two phases of the three-phase bridge inverter circuit 20 are turned on, the switch tube connected in series with the power resistance in the corresponding connected RLC switch unit is turned off, there is one switch tube turned on at each end of the inductance and the two switch tubes are not in series, the inductance inhibits the pulse current, and the absorption resistance and the absorption capacitor perform transient action.

[0056] In addition, the method for operating described above further comprises:

[0057] When two phases of the three-phase bridge inverter circuit 20 are cut off, the switch tube connected in series with the power resistance in the corresponding connected RLC switch unit is turned on, there is one switch tube turned on at each end of the inductance and the two switch tubes are not in series, and the power resistance consumes the energy stored by the inductance.

[0058] Specifically, the two phases of the three-phase bridge inverter circuit 20 are turned on by turning on the corresponding switch tubes in the three-phase bridge inverter circuit 20; the two phases of the three-phase bridge inverter circuit 20 are cut off by cutting off the corresponding switch tubes in the three-phase bridge inverter circuit 20.

[0059] It should be noted that those skilled in the art can clearly understand the specific implementation process of the method for operating the low-ripple BLDC drive circuit described above, which can be referred to the corresponding description in the foregoing circuit embodiment, and for the convenience and brevity of description, it will not be repeated here.

[0060] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can easily think of various equivalent modifications or replacements within the technical range disclosed by the present application, and these modifications or replacements should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A low-ripple BLDC drive circuit, characterized in that, include: The system includes a control unit and an RLC switching circuit connected between a three-phase bridge inverter circuit and a three-phase DC motor. The control unit is connected to both the RLC switching circuit and the three-phase bridge inverter circuit. The RLC switching circuit includes at least three RLC switching units, and each of the three-phase output terminals of the three-phase bridge inverter circuit is connected to one of the RLC switching units between itself and the three-phase DC motor. Each RLC switching unit includes a switching transistor, a power resistor, an inductor, an absorption resistor, and an absorption capacitor. The switching transistor includes a first switching transistor, a second switching transistor, a third switching transistor, a fourth switching transistor, and a fifth switching transistor. The first switching transistor is connected in series with the power resistor. The absorption... A resistor is connected in series with the absorption capacitor; the second switch is connected in series with the third switch, and one end of the inductor is connected between the second switch and the third switch; the fourth switch and the fifth switch are connected in series, and the other end of the inductor is connected between the fourth switch and the fifth switch; the power resistor is connected in series with the first switch, and then connected in parallel with the series-connected second and third switches, the series-connected fourth and fifth switches, and the series-connected absorption resistor and the absorption capacitor, respectively. After being connected in parallel, they are connected to the three-phase bridge inverter circuit and the three-phase DC motor; the switch is connected to the control unit.

2. The low-ripple BLDC drive circuit according to claim 1, characterized in that, The switching transistor is a top-down switching transistor.

3. The low-ripple BLDC drive circuit according to claim 2, characterized in that, The switching transistor includes two. Connected NMOS transistor discrete device.

4. The low-ripple BLDC drive circuit according to claim 2, characterized in that, The switching transistor includes a common source. A high-performance NMOS transistor integrated device.

5. The low-ripple BLDC drive circuit according to claim 1, characterized in that, The three-phase bridge inverter circuit includes switching transistors VT1, VT2, VT3, VT4, VT5, and VT6; switching transistors VT1 and VT4 are connected in series; switching transistors VT2 and VT5 are connected in series; switching transistors VT3 and VT6 are connected in series; one end of one of the RLC switching units is connected between switching transistors VT1 and VT4; one end of another RLC switching unit is connected between switching transistors VT2 and VT5; and one end of a third RLC switching unit is connected between switching transistors VT3 and VT6.

6. The low-ripple BLDC drive circuit according to claim 1, characterized in that, The control unit includes a PWM control chip.

7. A method of operating a low-ripple BLDC drive circuit as described in any one of claims 1 to 6, characterized in that, include: The low-ripple BLDC drive circuit turns on two phases of the three-phase bridge inverter circuit each time. When two phases of the three-phase bridge inverter circuit are turned on, the switching transistors in the corresponding RLC switching units that are connected in series with the power resistors are turned off. There is a non-series switch on each end of the inductor. The inductor suppresses pulse current and absorbs the resistor. And the transient operation of the absorption capacitor.

8. The operating method of a low-ripple BLDC drive circuit according to claim 7, characterized in that, Also includes: When one phase of the three-phase bridge inverter circuit is cut off, the switch in the corresponding RLC switching unit connected in series with the power resistor is turned on. There is a switch on each end of the inductor and the two switches are not connected in series. The power resistor consumes the energy stored in the inductor.

9. The operating method of a low-ripple BLDC drive circuit according to claim 8, characterized in that, Turning on two phases of a three-phase bridge inverter circuit is achieved by turning on the corresponding switching transistors in the three-phase bridge inverter circuit; turning off two phases of a three-phase bridge inverter circuit is achieved by turning off the corresponding switching transistors in the three-phase bridge inverter circuit.

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